Tsunamis

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Tsunami Causes

There are three causes of a tsunami: 

1. Tectonic displacemeny of ocean floor (under water earthquake) - eg Boxingday 2004 

2. Volcanic Eruption - eg Krakatoa 1883

3. Major Landslides - eg Prince William Sound, Canada, 1964

The most common cause is earthqaukes - 90% of tsunamis are generated in the pacific ocean at destructive playe boundaries. 

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How is a Tsunami formed?

When an earthqauke occours underwater, one plate is forced upwards suddenly, displacing all the water about it. 

1. Low and fast waves are sent out in all directions. These waves have a wave length of 100-1000km and travel up to 600mph

2. As the wave enters shallow water, it begins to slow down due to increased friction with the sea floor surface. This reduction in speed causes the wave to compress and gain height. 

3. As the waves slow and gain height waves moving faster behind catch up, and so wave length decreased to 10km. 

4. When the wave reaches the coast, it is 25m high. This is because as the waves have caught up with each other they have become one large wall of water. The first wave to hit is usually the largest for thsi reason. 

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Characteristics of Tsunamis

- Japanese for 'habour wave' 

- Low in hight in open water but taller in shallow water (20x higher) 

- Very fast moving in open water but slower in shallow waters 

- Unlike regular waves that travel in a circular motion, they travel in a stright line. 

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Boxing Day Tsunami 2004

Causes: 

9.0 earthqauke off the coast of Andaman Islands, at the time this was the biggest recorded earthquake. 

20miles under water in the Indian Ocean, a thrust fault was crate as a plate rose 40ft up across a 1000km stretch, 

When the tsunami hit the coast it had the force of three hurricanes. The tsunami had so much energy it travelled around the world three times. 

Due to the spatial extent some areas were worse affected than others as coastlines had varying degree of warning. 

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Boxing day Tsunami 2004

Warnings? 

Scientists were able to establist Southern Asia was going to be hit but the tsunami spread so fast these waring were too late. In Thailand the warnings were broadcast after the tsunami had hit. 

The time of day (night time) also meant many people were asleep and did not recieve warnings. 

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Boxing Day Tsunami 2004

Primary Effects: 

- 290,00 killed or missings. The number is still unknown

- Vegetation and topsoil removed up to 800m inland, disrupting agriculture. 

- Infrstructure, islands such as Andaman were cut off as jetties destroyed making aid getting in difficult. 

- Coastal cities devastated. 

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Boxing Day Tsunami 2004

Secondary Effects: 

- 500,000 forced to live in refugee camps in Indonesia alone. 

- economy of Southern Asian nations devastated as main industries destroyed; fishing, agriculture, tourism. 

- Water supplies and soils contaminated with salt from the sea water. 

- Increased the gap between rich and poor as the poor had no way of recovering and just become poorer

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Boxing Day Tsunami 2004

Responses: 

Immediate 

- International relief efforts were established, over 160 aid organisations and UN agencies responded. 

- Foriegn Military troops provided assistance, for exampe australian air control helped navigate aid to isolated areas. US hospital ships provided. 

Long Term: 

- Still people living in aid provided tents a year after. 

- Political barries had to be over come to allow aid into areas eg Sri Lanka civil war

- Tourist resorts quickly rebuilt by rich companies, at teh expense of fishing villages. 

- Introductions of tsunami education, practice drills and vunerability of coastal areas mapped. 

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Tokoku earthquake and tsunami 2011.

Causes: 

- 8.9 earthquake off the coast of Japan's largest island

- the pacific plate being subducted under the eurasian plate. 

- Massive ip thrust of plate forced water upwards and outwards creating the tsunami. 

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Tokoku earthquake and tsunami 2011.

Warnings? 

- A warning system kicked in warning a 300km stretch of coast but due to the proximity of the earthquake to land (70m) people had little time to prepare. 

- 1st wave hit 30 minutes after earthquake, a total of ten waves hit, each 1km apart. 

- The tsunami was too strong for the existing tsunami defenses. 

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Tokoku earthquake and tsunami 2011.

Impacts: 

Short term: 

- 16,000 deaths, 500,00 homes destroyed (due to Japans high density coastal population) 

- Nuclear powerplant meltdown (Fukushima) dangerous levels of radiation escaped and further 200,000 people evacuated. 

- Whole towns destroyed, 10,000 people missing

- Destruction of power lines

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Tokoku earthquake and tsunami 2011.

Long Term: 

- Schools closed

- Fishing sector destroyed

- Forced migration

- food and energy supplies cut off. 

- Dip in Japan's GDP as it was unable to maintain its manufacturing out put of cars/technology. 

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Tokoku earthquake and tsunami 2011.

Responses: 

- 116 countries and 28 international organisations offered or sent assistance. 

- Motorways repaired as quickly as 6 days after the earthquake allowing aid to easily transported around. 

- Japanese government made specially trained people availble eg The Self Defense Forces, to help with the domestic responses ( resuce) 

- Shelters set up for those who had lost their home in regional capitols. But people trapped in coastal towns could not reach them. 

- different goveernments giving different information about the safety of nuclear meltdown lead to confusion. 

- now scientists focused on the plate boundary south, next to tokyo, where a similar even could occour and devastate the capitol of Japan. 

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